Exhaust manifold

ABSTRACT

An exhaust manifold has a first upstream pipe connected to an exhaust ports of a group of cylinders of within an engine; a second upstream pipe connected to exhaust ports of cylinders other than the group of cylinders; and a merging pipe that merges the downstream ends of the first and second upstream pipe. The first upstream pipe is formed by a plurality of pipes and each pipe of the plurality of pipes forms a separate exhaust path that extends from the exhaust ports to the inside the merging pipe, and the second upstream pipe encloses the plurality of pipes and forms, between an inner surface of the second upstream pipe and an outer surface of the plurality of pipes, a plurality of exhaust paths that extend from the exhaust ports other than the exhaust ports of the group of cylinders to the inside of the merging pipe.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2006-306653 filed on Nov. 13, 2006, including the specifications, drawings, and abstract, is incorporated herein by reference in its entirety

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust manifold, and particularly to an exhaust manifold having an outer pipe shell construction.

2. Description of the Related Art

In general, in a multi-cylinder internal combustion engine (hereinafter, simply referred to as “engine”) of a vehicle, an exhaust manifold is provided, which collects the exhaust pipes from exhaust ports of each cylinder together and introduces the exhaust gas to a sound-muffling apparatus (hereinafter, “muffler”). The exhaust gas from the exhaust manifold is purified by a downstream catalytic device before being discharged.

In two revolutions of a 4-cycle engine, because exhausting of all cylinders is usually performed in a prescribed combustion sequence, for example, in the sequence of the first cylinder, the third cylinder, the fourth cylinder, and then the second cylinder, the periods of opening of exhaust valves having neighboring combustions, by partial overlapping (referred to as exhaust stroke overlapping) causes cases in which a load occurs caused by exhaust interference. Given this, known conventional art exists in which cylinders having no overlapping of distanced exhaust value opening time periods (hereinafter non-overlapping exhaust strokes) are treated as one group, exhaust paths at positions relatively close to the exhaust ports of these cylinders being collected by groups to reduce the number of pipe paths, and exhaust paths of cylinders having exhaust stroke overlapping and being positioned greater than a certain distance that allows suppression of exhaust interference being grouped together.

Additionally, conventional art in which a pair of sheet metal members are hermetically joined in the form of two half-shells to reduce the cost and the weight of an exhaust manifold.

In a conventional exhaust manifold of this type, a dual construction is made in which a cover that, for example, hermetically covers four independent pipes of an exhaust manifold, wherein at the time of starting and the like the exhaust gas is maintained at a high temperature to improve the performance of the catalyst in warming up to the activation temperature (refer, for example, to Japanese Patent Application Publication No. 2005-076605).

There is also art in which a branching pipe that connects to a group of cylinders having non-overlapping exhaust strokes, and a branching pipe that connects to a remaining group of cylinders having non-overlapping exhaust strokes are partitioned even within a merging pipe to suppress exhaust interference (refer, for example, to Japanese Patent Application Publication No. 2000-027642 and Japanese Patent Application Publication No. 9-068040).

Additionally, there is art in which, on the inside of an outer pipe shell having a shape that connects to all exhaust pipes, an inner pipe made as a bifurcated pipe that connects to only cylinders of a group on the inner side in the direction of arrangement of cylinders is provided to reduce the cost and reduce the weight by simplification (refer, for example, to Japanese Patent Application Publication No. 2001-065340).

However, in a conventional exhaust manifold having a single-pipe construction of two half-shells, there is not only the problem of exhaust interference causing a lowering of torque performance in the low-rpm range, but also the problem of poor heat insulation resulting in poor catalyst warm-up performance.

Also, in a conventional exhaust manifold in which independent pipes for all cylinders are provided within the shell or cover forming an outer pipe, the number of parts is large and the construction is a complex double construction, resulting in the problem of a high manufacturing cost.

Additionally, in a conventional exhaust manifold in which a branching pipe is provided inside an outer pipe, there is not only the problem of the processing of the inner pipe being difficult and a restriction tending to be placed on the degree of freedom of the shape thereof, but also the problem of difficulty in achieving good catalyst warm-up performance because of differences in the heat insulation performance between exhaust paths inside and outside the inner pipe.

SUMMARY OF THE INVENTION

The present invention provides a low-cost exhaust manifold featuring not only simple construction and light weight, but also improves torque and catalyst warm-up performance in a low-rpm range.

A first aspect of the present invention is an exhaust manifold having a first upstream pipe connected to exhaust ports of a group of cylinders within an engine; a second upstream pipe connected to exhaust ports of cylinders other than the group of cylinders; and a merging pipe that merges the downstream ends of the first upstream pipe and the second upstream pipe. In this exhaust manifold, the first upstream pipe is formed by a plurality of pipes and each pipe of the plurality of pipes forms a separate exhaust path that extends from the exhaust port of the group of cylinders to the inside the merging pipe, and the second upstream pipe encloses the plurality of pipes and forms, between an inner surface of the second upstream pipe and an outer surface of the plurality pipes, a plurality of exhaust paths that extends from the exhaust port other than the exhaust port of the group of cylinders to the inside of the merging pipe.

In this configuration, the plurality of pipes (independent pipes), which are the first upstream pipe, each forms a plurality of exhaust paths from the exhaust port of a group of cylinder to the inside the merging pipe 13, and the first and second upstream pipes each forms a plurality of exhaust paths from the remaining exhaust ports in the second upstream pipe to the inside the merging pipe 13. Therefore, because the plurality of pipes extend from the respective exhaust ports of each group of cylinders to the inside the merging pipe, heat exchange between exhaust gas flowing in the first and second upstream pipes is promoted, and a decrease in the catalyst warm-up performance is suppressed. In addition to a simple construction and a light weight, it is easy to process the plurality of pipes (independent pipes), and because it is not necessary to have independent pipes for all the cylinders, there is not much restriction on the degree of freedom of the shape of the independent pipes, and it is possible to reduce the manufacturing cost.

In the first aspect, each pipe of the plurality of pipes may be connected to the exhaust port of the group of cylinders having exhaust strokes that are mutually distanced.

By this configuration, exhaust interference between cylinders having adjacent exhaust strokes is suppressed, as is a decrease in the torque performance at low rpm speeds.

In the first aspect, each pipe of the plurality of pipes may be respectively connected to an export port of the cylinders positioned at the ends of a cylinder block.

By the above-noted configuration, the construction is substantially a dual-pipe configuration at both end parts in the cylinder row arrangement direction, in which the surface area coming into contact with the outside air is increased, the heat insulation performance at the end parts in the cylinder row arrangement direction being improved, the heat exchange between the plurality of exhaust paths is promoted, and the warm-up performance of the catalyst is improved.

In the first aspect, the engine may be an in-line 4-cylinder engine, and each pipe of the plurality of pipes may be respectively connected to the exhaust port of the first cylinder and the fourth cylinder of the in-line 4-cylinder engine.

By the above-noted configuration, the construction is substantially a dual-pipe configuration at the first and fourth cylinders at which the surface area in contact with the outside air is increased, the heat insulation performance of the exhaust paths connected to the exhaust ports of the first and fourth cylinders is improved, heat exchange between both exhaust paths and the exhaust path connected to the exhaust port of the second and third cylinders is promoted, and the catalyst warm-up performance is improved.

In the first aspect, the engine may be an in-line 4-cylinder engine, and each pipe of the plurality of pipes may be respectively connected to the exhaust port of a second cylinder and a third cylinder of the in-line 4-cylinder engine.

In the above-noted configuration as well, not only is the construction simple and the weight reduced, but also it is easy to process the inner pipe and there is not much restriction on the degree of freedom of the shape thereof. Also, because the plurality of pipes (independent pipes) extend respectively from the inside the second upstream pipe to the inside the merging pipe, heat exchange between the exhaust gases that pass through the first and second upstream pipes is promoted, and a decrease in the warm-up performance of the catalyst is suppressed.

In the first aspect, each pipe of the plurality of pipes may form a fan-shaped aperture plane adjacently in the merging pipe, and semicircular or fan-shaped aperture plane corresponding to a downstream end of the exhaust path of the second upstream pipe may be formed in the merging pipe.

By the above-noted configuration, by appropriately establishing the downstream end shape of the plurality of pipes (independent pipes), it is possible to set the downstream ends of the first upstream pipe and the downstream end of the exhaust path inside the second upstream pipe to the desired shapes. Additionally, it easy to set the heat exchange region that is desired between the exhaust paths.

In the first aspect, a gap may be formed between the plurality of pipes (independent pipes) and the second upstream pipe, and a heat-insulating spacer may be provided within the gap.

By the above-noted configuration, it is possible, while placing the minimal intervening heat-insulating layer between the first and second upstream pipes, to suppress mechanical interference between the first and second upstream pipes.

In the first aspect, the second upstream pipe may be formed by a pair of sheet metal members that sandwich the first upstream pipe and that are hermetically joined each other.

By the above-noted configuration, it is easy to manufacture an exhaust manifold with a dual-pipe construction in which a first upstream pipe is disposed inside a second upstream pipe that serves as the outer pipe, and further possible to reduce the cost of manufacturing.

In the first aspect, the merging pipe may be formed by the pair of sheet metal members integrated with the second upstream pipe.

By the above-noted configuration, it is easy to manufacture an exhaust manifold having a dual-pipe construction with an integrated merging pipe and second upstream pipe using sheet metal, and further possible to reduce the cost of manufacturing.

A second aspect of the present invention is an exhaust manifold having a first upstream pipe connected to at least one exhaust port of a plurality of cylinders of an engine; a second upstream pipe connected to the exhaust port of a cylinder other than the cylinders connected to the first upstream pipe; and a merging pipe that merges the downstream ends of the first upstream pipe and the second upstream pipe. In the second aspect, the first upstream pipe forms a separate exhaust path that extends from the exhaust port of the cylinders to inside the merging pipe, and the second upstream pipe encloses the first upstream pipe and forms, between an inner surface of the second upstream pipe and an outer surface of the first upstream pipe, an exhaust path that extends from the exhaust port of the cylinder that is not connected to the first upstream pipe to the inside of the merging pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features, and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, and wherein:

FIG. 1 is a front view showing the general configuration of an exhaust manifold according to a first embodiment of the present invention;

FIG. 2 is a front view, seen in the condition with one shell cover removed, showing the general configuration of the inside of the exhaust manifold of the first embodiment of the present invention;

FIG. 3 is view of the exhaust manifold according to the first embodiment of the present invention, viewed in the direction of the arrow III in FIG. 1;

FIG. 4 is a view of the exhaust manifold according to the first embodiment of the present invention, viewed in the direction of the arrows IV-IV in FIG. 1;

FIG. 5 is a partially enlarged cross-sectional view describing the inner construction and heat-insulating layer of one group of upstream pipes of the exhaust manifold according to the first embodiment of the present invention;

FIG. 6 is a graph comparing the difference in the operating effect of the exhaust manifold according to the first embodiment of the present invention with the pulsation pressure of an exhaust port according to conventional art, in which the vertical axis is exhaust port pulsation pressure and the horizontal axis is the crank angle;

FIG. 7 is a drawing describing the exhaust interference suppressing effect of the exhaust manifold according to the first embodiment of the present invention;

FIG. 8 is a graph comparing the difference in the operating effect of the exhaust manifold according to the first embodiment of the present invention with the engine torque according to conventional art, in which the vertical axis is the engine torque and the horizontal axis is the engine rpm speed;

FIG. 9 is a front view showing the general configuration of an exhaust manifold according to a second embodiment of the present invention;

FIG. 10 is a front view showing the general configuration of the inner part of the exhaust manifold according to the second embodiment of the present invention in the condition in which one shell cover is removed;

FIG. 11 is a side view showing the general configuration of the exhaust manifold according to the second embodiment of the present invention; and

FIG. 12 is a drawing showing the general configuration of the exhaust manifold according to the second embodiment of the present invention, illustrating the aperture shape as seen from therebelow.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are described below, with reference made to the accompanying drawings.

FIG. 1 to FIG. 5 show an exhaust manifold according to the first embodiment of the present invention.

As show in FIG. 1 to FIG. 3, the exhaust manifold 10 of the first embodiment includes a first upstream pipe 11, which has a plurality of exhaust intake ports 11 i, 11 j that are each connected to exhaust ports of one group of cylinders (for example the exhaust port 1 a of the first cylinder and the exhaust port 1 d of the fourth cylinder) of a plurality of cylinders of an in-line 4-cylinder engine 1 (details not illustrated), a second upstream pipe 12, which has a plurality of exhaust intake ports 12 i, 12 j that are each connected to exhaust ports of the cylinders that are not connected to the first upstream pipe 11 (for example the exhaust port 1 b of the second cylinder and the exhaust port 1 c of the third cylinder) of the plurality of cylinders of the engine 1, a merging pipe 13 that is substantially cylindrical in shape and that merges the downstream ends of the first upstream pipe 11 and the second upstream pipe 12, an upstream flange 14 that is fixed to the cylinder head of the engine 1 (the part of the engine 1 illustrated in FIG. 1), and a downstream flange 15 that is connected, via a catalytic device 50 (only part of which is illustrated), to a downstream exhaust pipe and muffler, which are not illustrated.

Although the part surrounding the exhaust port that serves as the mechanical connection (link) with the exhaust manifold is also called an exhaust manifold, in this case it means the part that forms the exhaust ports of the engine block. Also, although the upstream flange 14 and the downstream flange 15 are shown in simplified form as rectangles or circles, the actual shapes differ from those shown, and have linking bolt holes and the like. It will be understood that the first upstream pipe 11 and the second upstream pipe 12 are curved. Additionally, although the in-line 4-cylinder engine 1 in the first embodiment is described as a 4-cycle gasoline engine having the combustion sequence of the first cylinder, the third cylinder, the fourth cylinder, and then the second cylinder, the combustion sequence may be a different sequence that enables smooth rotation of the crank. The present invention is not restricted to 4-cylinder gasoline engines.

The first upstream pipe 11 is formed by a plurality of independent pipes 21, 22. As shown in FIG. 2 and FIG. 5, the independent pipes 21, 22 are each housed inside the second upstream pipe 12, via an intervening gap-like heat-insulating layer 41 (gap), and each form the plurality of independent exhaust paths 11 a, 11 b (one group of a plurality of exhaust paths) from the exhaust port 1 a and the exhaust port 1 d (exhaust port of one group of cylinders) up to the merging pipe 13.

The second upstream pipe 12 is in the shape of a shell made of opposing half-shells, formed of a prescribed stainless steel sheeting having a thickness of, for example, approximately 1.5 mm to 2.0 mm. That is, the second upstream pipe 12 is formed by the shell covers 31 and 32, which are made of a plurality of sheet metal members hermetically joined in mutual opposition so as to sandwich the first upstream pipe 11.

More specifically, the second upstream pipe 12 is formed by channel-shaped shell covers 31, 32, which are two stainless steel sheets. The shell covers 31, 32 are formed by pressing and, having the peripheral shapes as shown in FIG. 1 (polyfurcated shape branched into four). The surfaces that form the outer contour lines of the shell covers 31, 32 are curved surfaces along contour joining surface 12 c shown in FIG. 3. The inner concave surfaces of the shell covers 31, 32 oppose the contour joining surface 12 c, and the outer peripheral contour part (excluding the parts forming exhaust intake ports and exit ports) is hermetically joined by welding or the like. In this manner; the second upstream pipe 12 and the merging pipe 13 are integrally formed by the shell covers 31, 32. The upstream flange 14 and the downstream flange 15 are respectively integrally joined and fixed to the upstream end and the downstream end of the second upstream pipe 12 by welding or the like.

The independent pipes 21, 22 may be made of, for example, stainless steel pipe having a material thickness of 1.5 mm to 2.0 mm, the downstream ends of which, positioned inside the merging pipe 13, are formed into a specific cross-sectional shape, to be described below, and the upstream ends of which are circular in cross-section. The cross-sectional shapes of the intermediate parts of the independent pipes 21, 22 are arbitrary. For example, of the independent pipes 21, 22 the parts in the vicinity of the merging pipe 13 have a specific cross-sectional shape (for example, a fan shape) that changes to a cross-sectional shape that approaches being cylindrical when approaching the upstream side from the merging pipe 13. Alternatively, to prevent that the contacting surfaces of exhaust paths 12 a, 12 b (to be described in detail below) inside the second upstream pipe 12 increase and also so that there is no sudden change in the cross-sectional shape of the intermediate part of the exhaust paths 12 a, 12 b from inside the second upstream pipe 12 to inside the merging pipe 13, the cross-section of the independent pipes 21, 22 may be made substantially D-shaped or substantially crescent-shaped. While the independent pipes 21, 22 may be single steel pipes with no joints, they may also be made by the airtight joining of a plurality of pipes or channel-shaped pipe wall members having shapes that are substantially arcs.

When the shell covers 31, 32 of the second upstream pipe 12 are joined by welding or the like, both ends of the independent pipes 21, 22 become integrally joined to the second upstream pipe 12 as a result. The parts of the independent pipes 21, 22 other than the joining part with the second upstream pipe 12, that is, the intermediate parts of the independent pipes 21, 22, are separated from the shell covers 31, 32 of the second upstream pipe 12 by a prescribed gap, thereby forming a heat-insulating layer of a prescribed thickness, described below, between the independent pipes 21, 22 and the shell covers 31, 32. The heat-insulating layer is a non-contacting part or a part that is formed by the insertion of a heat-insulating spacer, so that heat conduction is substantially cut off.

As shown in the partially enlarged view of FIG. 2 and FIG. 5, a mesh member 42 made of, for example, a metal mesh, is inserted as a heat-insulating spacer in the heat-insulating layer 41 between the independent pipes 21, 22 of the first upstream pipe 11 and the shell covers 31, 32 of the second upstream pipe 12. The mesh member 42 permits relative displacement between the independent pipes 21, 22 and the shell covers 31, 32 caused by a temperature difference between the shell covers 31, 32 of the second upstream pipe 12, which are in contact with the outside air, and the independent pipes 21, 22, which are exposed to exhaust gas from the engine 1 inside the second upstream pipe 12, or caused by mechanical vibration and the like, and maintain the thickness of the heat-insulating layer 41 between the opposing parts at the minimum thickness level required to cut off conduction of heat therethrough.

The mesh member 42 is inserted, for example, at a location at which the heat-insulating layers 41 surround the independent pipes 21, 22 of the four cylindrical parts at the upstream side of the second upstream pipe 12, with a thickness that is the distance separating the closest approaching parts of the independent pipes 21, 22 and the shell covers 31, 32, and supported by either the independent pipes 21, 22 or the shell covers 31, 32. In the case of having the mesh member 42 supported by the shell covers 31, 32, a channel depression or guide rib or the like may be formed in the shell covers 31, 32 so as to guide the mesh member 42.

By the independent pipes 21, 22 of the first upstream pipe 11 and the shell covers 31, 32 of the second upstream pipe 12 as described above, a plurality of exhaust paths 12 a, 12 b (other plurality of exhaust paths) extending from the exhaust port 1 c of the third cylinder and the exhaust port 1 b of the second cylinder to inside the merging pipe 13 are formed inside the second upstream pipe 12.

In this case, it will be understood that the shape of the shell covers 31, 32 may be arbitrarily set so as to partition the exhaust paths 12 a and 12 b, and that the depth of the branching point of the upstream branching part 12 d of the second upstream pipe 12 between the exhaust paths 12 a and 12 b may be set in accordance with the required characteristics of the engine. That is, by appropriately setting the shape of the shell covers 31, 32, the location of the branching point of the upstream branching part 12 d, the thickness of the heat-insulating layer 41, and the location of the mesh member 42, it is possible to form the exhaust paths 12 a, 12 b as substantially independent paths.

Also, the exhaust paths 11 a, 11 b inside the independent pipes 21, 22 that form the first upstream pipe 11 are connected to the exhaust port of one group of cylinders of the plurality of cylinders of the engine 1, for example, the exhaust port 1 a of the first cylinder and the exhaust port 1 d of the fourth cylinder. The exhaust port 1 a of the first cylinder and the exhaust port 1 d of the fourth cylinder are a group of exhaust ports of cylinders of the plurality of cylinders of the engine 1 that have mutually non-overlapping exhaust strokes. Similarly, the exhaust paths 12 a, 12 b inside the second upstream pipe 12 are connected to the exhaust ports of other cylinders of the plurality of cylinders of the engine 1, for example, exhaust port 1 b of the second cylinder and exhaust port 1 c of the third cylinder. The exhaust port 1 b of the second cylinder and the exhaust port 1 c of the third cylinder are a group of exhaust ports of cylinders of the plurality of cylinders of the engine 1 that have overlapping exhaust strokes. The cross-sectional area and merging angle (angle of inclusion between the exhaust paths 11 a and 11 b forming the introduction part into the merging pipe 13) and the like may be set in accordance with the particular characteristics of the engine.

Additionally, because the plurality of independent pipes 21, 22 are connected to the exhaust ports 1 a, 1 d of the first and fourth cylinders at the end parts of the row of cylinder of the engine 1, the independent pipes 21, 22 of the first upstream pipe 11 and the shell covers 31, 32 of the second upstream pipe 12 have a dual-pipe construction that surrounds the heat-insulating layer 41 at the end part of the row of cylinders. Although in this case, the “end part in the row of cylinders” refers to the first cylinder and the fourth cylinder in the case of an in-line 4-cylinder engine, this expression means the parts at both ends in the direction of each row of cylinders of the cylinder block.

As shown in FIG. 4, the plurality of independent pipes 21, 22 form fan-shaped apertures that are mutually neighboring inside the merging pipe 13, for example, forming the substantially quarter-circular apertures 11 e, 11 f, and a semicircular aperture 12 e opposing the downstream end of the exhaust ports 12 a, 12 b inside the second upstream pipe 12 is formed inside the merging pipe 13. The shapes of the apertures 11 e, 11 f are substantially equal divisions of the circular cross-section of the inside of the merging pipe 13 derived by dividing by the number of exhaust ports connecting with the inside of the merging pipe 13, which in this case is the number of the exhaust paths 11 a, 11 b, 12 a, and 12 b, this differing depending upon the number of cylinders of the engine.

Also, the shape of the aperture 12 e in the case in which the exhausts from all the cylinders of in-line 4-cylinder engine are merged in the merging pipe 13 is, for example, substantially semicircular. The shape of the aperture 12 e may be fan-shaped, rather than semicircular. In the case of forming a dual exhaust, the apertures 11 e, 11 f each have semicircular cross-sections forming a circular cross-section together, the aperture 12 e being able to have an outer annular shape that encloses the apertures 11 e, 11 f, or in reverse, the apertures 11 e, 11 f may each have semicircular cross-sections to form an outer annular shape together, with the aperture 12 e being able to form a path having a circular cross-section in the center thereof.

The catalytic device 50 forms a part of the exhaust path continuing downstream from the merging pipe 13 and houses a known three-way catalyst 51 therewithin, the catalytic device 50 being one that reduces or oxidizes harmful substances such as nitrogen oxides in the exhaust gas, converting them to harmless substances such as water, carbon dioxide, and nitrogen. By controlling the air-fuel ratio of the engine to within a prescribed range, the three-way catalyst maintains the oxygen concentration of the exhaust gas within a certain range, thereby achieving highly efficient exhaust gas purification. In the catalytic device 50, the three-way catalyst usually has a low reducing capacity at normal temperatures and is easily damaged if continuously exposed to excessive heating or vibration. For this reason, although it is necessary to warm up the catalytic device 50 by the heat of the exhaust gas so as to quickly reach the activation temperature when the engine is started, when the reducing capacity is low, it is a device that is not easily mounted immediately after the exhaust port. Also, the catalytic device 50 may be a different type of exhaust gas purification device that requires control of exhaust temperature from the standpoint of performance.

The operating effect will now be described.

When the engine 1 is operating, the intake stroke, compression stroke, combustion and expansion stroke, and the exhaust stroke are repeated in a prescribed combustion sequence for all cylinders from the first cylinder to the fourth cylinder. For example, when the first cylinder is in the combustion and expansion stroke, the second through fourth cylinders are substantially in the exhaust stroke, the compression stroke, and the intake stroke, respectively. When the first cylinder is in the exhaust stroke, the second through the fourth cylinders are substantially in the intake stroke, the combustion and expansion stroke, and the compression stroke, respectively. When the first cylinder is in the intake stroke, the second through the fourth cylinders are substantially in the compression stroke, the exhaust stroke, and the combustion and expansion stroke, respectively. When the first cylinder is in the compression stroke, the second through the fourth cylinders are substantially in the combustion and expansion stroke, the intake stroke, and the exhaust stroke, respectively.

In an exhaust manifold 10 according to the first embodiment configured as described above and installed in the engine 1, the plurality of independent pipes 21, 22, which are the first upstream pipe 11 from a plurality of exhaust paths 11 a, 11 b, respectively, from the exhaust ports 1 a, 1 d of the first and fourth cylinders (one group of cylinders) up to inside the merging pipe 13. The independent pipes 21, 22 of the first upstream pipe 11 and the second upstream pipe 12 form, respectively, the plurality of exhaust paths 12 a, 12 b from the exhaust ports of the second and third cylinders (remaining cylinders) inside the first upstream pipe 11 and also outside the independent pipes 21, 22. Therefore, heat exchange is promoted between exhaust gas passing from the independent pipes 21, 22 and through the exhaust paths 11 a, 11 b inside the first upstream pipe 11 and exhaust gas passing through the exhaust paths 12 a, 12 b inside the second upstream pipe 12 formed between the second upstream pipe 12 and the independent pipes 21 and 22, and the desired warm-up performance of the catalytic device 50 at the time of starting is achieved. Also, with respect to the four cylinders, there are only the two independent pipes 21, 22 as inner pipes of the exhaust manifold 10, thereby simplifying the construction and reducing the weight. Additionally, the processing of the independent pipes 21 and 22, which are made of steel pipes without joints and having a relatively thin wall thickness is facilitated, and the restriction on the three-dimensional degree of freedom of the piping shape is eliminated by halving of the number of independent pipes. It is, therefore, possible to reduce the cost of manufacturing the exhaust manifold 10.

Because the plurality of independent pipes 21, 22 connect to a group of cylinders of the plurality of cylinders of the engine 1 having exhaust strokes that do not overlap, for example, the exhaust ports 1 a, 1 d of the first cylinder and the fourth cylinder, exhaust interference is suppressed between two cylinders having a combustion sequence such that the exhaust strokes thereof overlap, such as the first cylinder and the third cylinder, thereby suppressing a reduction in the torque performance of the engine 1 at low rpm speeds.

Also, the independent pipes 21, 22 connect to the cylinders positioned at the ends of the row of cylinders of the plurality of cylinders of the engine 1, for example, to the first cylinder and the fourth cylinder of a in-line 4-cylinder engine and form, together with the second upstream pipe 12, which is the outer shell, a dual-pipe construction at both ends in the direction of the row of cylinders. The result is that, because of an improvement in the heat insulation of the exhaust paths 11 a, 11 b on the inside of the independent pipes 21, 22, which are the inner pipes, and the decrease of a difference in heat-insulation performance relative to the exhaust paths 12 a, 12 b on the outside thereof, the warm-up performance of the catalytic device 50 is improved.

Additionally, in the exhaust manifold 10 of the first embodiment, in addition to the plurality of independent pipes 21, 22 forming fan-shaped apertures 11 e, 11 f that are mutually neighboring inside the merging pipe 13, because a semicircular or fan-shaped aperture 12 e is formed to correspond to the downstream end of the exhaust paths 12 a, 12 b inside the second upstream pipe 12 in the merging pipe 13, by merely appropriately establishing the downstream end shape of the independent pipes 21, 22, it is possible to set the downstream ends of the exhaust paths 11 a, 11 b inside the first upstream pipe 11 and the downstream ends of the exhaust paths 12 a, 12 b inside the second upstream pipe 12 to the desired shapes. Additionally, it is easy to establish a desired heat exchange region between the exhaust paths 11 a, 11 b and the exhaust paths 12 a, 12 b.

Additionally, in the first embodiment a mesh member 42, which is a heat-insulating spacer, is provided in the heat-insulating layer 41 between the plurality of independent pipes 21, 22 of the first upstream pipe 11 and the shell covers 31, 32 of the second upstream pipe 12. By doing this, even if the thickness of the heat-insulating layer 41 between the first upstream pipe 11 and the second upstream pipe 12 is minimized, it is possible to suppress mutual mechanical interference accompanying contact between the first upstream pipe 11 and the second upstream pipe 12.

In addition, the exhaust manifold 10 of the first embodiment has a construction in which the second upstream pipe 12 and the substantially cylindrical merging pipe 13 are integrated by a plurality of shell covers 31, 32 joined hermetically in mutual opposition so as to sandwich the first upstream pipe 11. By doing this, it is possible to dispose the first upstream pipe 11 inside the second upstream pipe 12 that serves as the outer pipe and to easily manufacture an exhaust manifold 10 having a dual-pipe construction with an integrated merging pipe 13, enabling a reduction of the manufacturing cost thereof.

FIG. 6 and FIG. 7 are graphs showing the results of comparing the exhaust port pulsation pressure at a position 70 mm from the upstream end of the exhaust intake of an exhaust manifold having a single-pipe construction by the conventional dual half-shells and the exhaust manifold 10 of the first embodiment of the present invention (shown by EMBODIMENT in the drawings) having the above-described configuration. The exhaust port pulsation pressure shown in these graphs is the result of calculated simulation of the exhaust port pressure at prescribed crank angle positions over a period of two revolutions, under the same conditions for each configuration in common.

Part of FIG. 6 is shown in enlarged form in FIG. 7. The exhaust port pulsation pressure of the first embodiment of the present invention as shown by the thick solid line in FIG. 7 does not exhibit the increase in the exhaust port pressure caused by exhaust interference such as exhibited by the exhaust manifold according to the conventional art shown by the thin solid line in FIG. 7, and it can be understood that the effect of reduction of the exhaust interference as shown by the hatched portion in FIG. 7 can be expected.

By virtue of the effect of reducing the exhaust interference, it is possible to expect an improvement in the output torque [Nm] of the engine at low rpm speeds such as shown in FIG. 8, and in the simulation results it is possible to expect an span of improvement in engine torque of approximately 1%. In reality it is thought that an even greater improvement in engine torque can be expected, and it is possible to expect a torque output and catalyst warm-up performance substantially equivalent to an in-line 4-cylinder gasoline engine having four independent pipes.

FIG. 9 to FIG. 12 show an exhaust manifold according to the second embodiment of the present invention.

In the above-described first embodiment, a plurality of independent pipes 21, 22 are provided in correspondence with the first cylinder and the fourth cylinder of an in-line 4-cylinder engine. The exhaust manifold of the second embodiment differs from the first embodiment in that the plurality of independent pipes are connected to the second cylinder and the third cylinder of the in-line 4-cylinder engine. Therefore, constituent elements that are one and the same as or that correspond to constituent elements of the first embodiment are described in FIG. 9 to FIG. 12 using the same reference numerals as in FIG. 1 to FIG. 5 for the corresponding element, and in the description that follows, the description of only the points of difference with respect to the first embodiment are described.

As shown in FIG. 9 to FIG. 12, the exhaust manifold 60 of the second embodiment includes a first upstream pipe 61, which has a plurality of exhaust intake ports 61 i, 61 j that are each connected to exhaust ports of one group of cylinders (for example the exhaust port 1 b of the second cylinder and the exhaust port 1 c of the third cylinder) of a plurality of cylinders of an in-line 4-cylinder engine 1, a second upstream pipe 62, which has a plurality of exhaust intake ports 62 i, 62 j that are each connected to exhaust ports of a remaining group of cylinders (for example the exhaust port 1 a of the first cylinder and the exhaust port 1 d of the fourth cylinder) of the plurality of cylinders of the engine 1, a merging pipe 63 that is substantially cylindrical in shape and that merges the downstream ends of the first upstream pipe 61 and the second upstream pipe 62, an upstream flange 14 that is fixed to the cylinder head of the engine 1, and a downstream flange 15 that is connected, via a catalytic device 50, to a downstream exhaust pipe and muffler, which are not illustrated.

The first upstream pipe 61 is formed by a plurality of independent pipes 71, 72, and forms exhaust paths 61 a, 61 b (one group of a plurality of exhaust paths) from the exhaust port 1 b of the second cylinder and the exhaust port 1 c of the third cylinder (exhaust ports of one group of cylinders) up to inside the merging pipe 13, which are housed inside the second upstream pipe 62 with an intervening gap-like heat-insulating layer (corresponding to the heat-insulating layer 41 in FIG. 5 and referred to hereinunder as the heat-insulating layer 41).

The second upstream pipe 62 is in the shape of a shell made of opposing half-shells, formed of a prescribed sheet metal, for example, a stainless steel sheet having a sheet thickness of approximately 1.5 mm to 2.0 mm. That is, the second upstream pipe 62 is formed by the shell covers 81 and 82, which are made of a plurality of sheet metal members hermetically joined in mutual opposition so as to sandwich the first upstream pipe 61. Specifically, the second upstream pipe 62 is formed by channel-shaped shell covers 31, 32, which are two stainless steel sheets. The shell covers 81, 82 are formed by pressing and have the peripheral contour shapes as shown in FIG. 9. The surfaces that forms the outer contour lines of the shell covers 81, 82 are curved surfaces along contour joining surface 62 c shown in FIG. 11. The inner concave surfaces of the channel-shaped shell covers 81, 82 oppose the contour joining surface 62 c, and the outer peripheral contour part (excluding the parts forming exhaust intake ports and exit ports) is hermetically joined by welding or the like, so that the second upstream pipe 62 and the merging pipe 63 are integrally formed by the shell covers 81, 82. The upstream flange 14 and the downstream flange 15 are respectively integrally joined to the upstream end and the downstream end of the second upstream pipe 62 by welding or the like.

The independent pipes 71, 72 of the first upstream pipe 61 are made of, for example, stainless steel pipe having a thickness of 1.5 mm to 2.0 mm, the downstream ends of which are formed into a specific cross-sectional shape, to be described below, and the upstream ends of which being circular in cross-section. The cross-sectional shapes of the intermediate parts of the independent pipes 71, 72 are arbitrary.

When the shell covers 81, 82 of the second upstream pipe 62 are joined by welding or the like, at least the upstream ends or both ends of the independent pipes 71, 72 are integrally joined to the second upstream pipe 62 by welding or the like. The parts of the independent pipes 71, 72 other than the joining part with the second upstream pipe 62, that is, the intermediate parts thereof, are spaced with respect to the shell covers 81, 82 of the second upstream pipe 62 by a prescribed gap, thereby forming a heat-insulating layer 41 of a prescribed layer thickness between the independent pipes 71, 72 and the shell covers 81, 82.

As shown in FIG. 12, the plurality of independent pipes 71, 72 form fan-shaped apertures that are mutually neighboring inside the merging pipe 63, for example, forming the substantially quarter-circular apertures 61 e, 61 f. Additionally, a substantially semicircular aperture 62 e corresponding to the downstream end of the exhaust paths 62 a, 62 b (other plurality of exhaust paths) inside the second upstream pipe 62 is formed inside the merging pipe 63. That is, in the second embodiment, in contrast to the above-described first embodiment, the exhaust paths 61 a, 61 b that communicate with the exhaust port of the second cylinder and the third cylinder each have the quarter-circular apertures 61 e, 61 f, and the exhaust paths 62 a, 62 b that communicate with the exhaust port of the first cylinder and the fourth cylinder have an integrated substantially semicircular aperture 62 e.

In the second embodiment, even if the plurality of independent pipes 71, 72 are provided in correspondence to the second cylinder and the third cylinder of the in-line 4-cylinder engine 1, not only is the construction of the exhaust manifold 60 simple, but also the processing of the independent pipes 71, 72, which are the inner pipes, is easy, and there is not much restriction on the degree of freedom with regard to the shape thereof. Additionally, the plurality of independent pipes 71, 72 extend up to the inside of the merging pipe 63 from the connection part with the exhaust ports 1 b, 1 c of one group of cylinders inside the second upstream pipe 62. By doing this, heat exchange is promoted between the exhaust gases passing through the first upstream pipe 61 and the second upstream pipe 62, and it is possible to suppress a worsening of the warm-up performance of the catalytic device 50. Therefore, even though there is a slight deterioration in heat insulation with respect to the first embodiment, it is possible to provide a low-cost exhaust manifold having not only a simple construction, but also improved torque performance and suppressed deterioration of warm-up performance in a low rpm range.

Although in each of the above-described embodiments the engine 1 is an in-line 4-cylinder engine, in the case of an in-line 6-cylinder engine, a second upstream pipe configuration may be envisioned that has one branching point from the first cylinder to the third cylinder and another branching point from the fourth cylinder to the sixth cylinder, each branching point being joined by a double half-shell that serves as the outer pipe, and one independent pipe centrally-placed in the cylinder row direction or two independent pipes distanced in the cylinder row direction being housed inside the second upstream pipe. That is, in the case of an in-line 6-cylinder engine in which the first cylinder to the sixth cylinder are arranged in a row in cylinder sequence, the configuration may be one in which a second upstream pipe is provided having an independent part corresponding to the first cylinder to the third cylinder of the in-line 6-cylinder engine and an independent part corresponding to the second cylinder and the fourth cylinder to the sixth cylinder. Additionally, the independent pipes may be connected to the exhaust port of at least one of the second cylinder and the fifth cylinder of the in-line 6-cylinder engine. Also, the independent pipe may be configured as a plurality of independent pipes, the plurality of independent pipes being respectively connected to at least one of the first and third cylinders and the fourth and sixth cylinders of an in-line 6-cylinder engine. Although in the above-described embodiments the second upstream pipe and the substantially cylindrical merging pipe are described as being integrally joined at both ends by welding or the like, one end may be in a sliding fit condition. Additionally, although the configurations are such that the shell-like second upstream pipe is integrated by a pair of shell covers together with a merging pipe, the merging pipe may be configured as a jointless cylindrical member, the second upstream pipe and merging pipe to which a pair of shell covers is joined in the direction of exhaust gas flow (axial direction). Also, rather than having a pair of opposing shell covers, the second upstream pipe may be configured using three or more pipe wall members.

As described above, in this embodiment a plurality of independent pipes are each housed inside a shell-like second upstream pipe, and extend from the connecting part with one group of exhaust ports up until the inside of the merging pipe. By doing this, it is possible to promote heat exchange between exhaust gas passing through the exhaust paths inside the upstream pipes. Additionally, this embodiment provides a low-cost exhaust manifold having simple construction and light weight, and also one that improves the catalyst warm-up performance, with ease of processing the inner pipe and without a great restriction on the degree of freedom regarding the shape thereof. In particular, by connecting the first upstream pipe to the exhaust ports of a group of cylinders of the plurality of cylinders of the engine having non-overlapping exhaust strokes, exhaust interference between cylinders having overlapping exhaust strokes is suppressed, and the reduction in torque at low rpm ranges is also suppressed. The present invention is effective for exhaust manifolds in general, and for an exhaust manifold having a outer pipe shell construction made of sheet metal in particular. 

1. An exhaust manifold comprising: a first upstream pipe connected to exhaust ports of a group of cylinders within an engine; a second upstream pipe connected to exhaust ports of cylinders other than the group of cylinders; and a merging pipe that merges the downstream ends of the first upstream pipe and the second upstream pipe, wherein the first upstream pipe is formed by a plurality of pipes and each pipe of the plurality of pipes forms a separate exhaust path that extends from the exhaust port of the group of cylinders to the inside the merging pipe, and the second upstream pipe encloses the plurality of pipes and forms, between an inner surface of the second upstream pipe and an outer surface of the plurality of pipes, a plurality of exhaust paths that extend from the exhaust port other than the exhaust port of the group of cylinders to the inside of the merging pipe.
 2. The exhaust manifold according to claim 1, wherein each pipe of the plurality of pipes that forms the first upstream pipe is connected to the exhaust port of the group of cylinders having exhaust strokes that are mutually distanced.
 3. The exhaust manifold according to claim 1, wherein each pipe of the plurality of pipes is respectively connected to an exhaust port of the cylinders positioned at the ends of a cylinder block.
 4. The exhaust manifold according to claim 3, wherein the engine is an in-line 4-cylinder engine, and wherein each pipe of the plurality of pipes is respectively connected to the exhaust port of the first cylinder and the fourth cylinder of the in-line 4-cylinder engine.
 5. The exhaust manifold according to claim 2, wherein the engine is an in-line 4-cylinder engine, and wherein each pipe of the plurality of pipes is respectively connected to the exhaust port of a second cylinder and a third cylinder of the in-line 4-cylinder engine.
 6. The exhaust manifold according to claim 1, wherein each pipe of the plurality of pipes forms a fan-shaped aperture plane adjacently in the merging pipe, and wherein semicircular or fan-shaped aperture plane corresponding to a downstream end of the exhaust path of the second upstream pipe is formed in the merging pipe.
 7. The exhaust manifold according to claim 1, wherein a gap is formed between the plurality of pipes and the second upstream pipe, and a heat-insulating spacer is provided within the gap.
 8. The exhaust manifold according to claim 1, wherein the second upstream pipe is formed by a pair of sheet metal members that sandwich the first upstream pipe and that are hermetically joined each other.
 9. The exhaust manifold according to claim 8, wherein the merging pipe is formed by the pair of sheet metal members integrated with the second upstream pipe.
 10. An exhaust manifold comprising: a first upstream pipe connected to at least one exhaust port of a plurality of cylinders of an engine; a second upstream pipe connected to the exhaust port of a cylinder other than the cylinders connected to the first upstream pipe; and a merging pipe that merges the downstream ends of the first upstream pipe and the second upstream pipe, wherein the first upstream pipe forms a separate exhaust path that extends from the exhaust port of the cylinders to inside the merging pipe, and the second upstream pipe encloses the first upstream pipe and forms, between an inner surface of the second upstream pipe and an outer surface of the first upstream pipe, an exhaust path that extends from the exhaust port of the cylinder that is not connected to the first upstream pipe to the inside of the merging pipe.
 11. The exhaust manifold according to claim 10, wherein the engine is an in-line 6-cylinder engine, and the second upstream pipe has a first part connected to the first cylinder to the third cylinder of the in-line 6-cylinder engine and a second part connected to the fourth cylinder to the sixth cylinder in the in-line 6-cylinder engine.
 12. The exhaust manifold according to claim 11, wherein the first upstream pipe connects to at least one of the second cylinder and the fifth cylinder of the in-line 6-cylinder engine.
 13. The exhaust manifold according to claim 11, wherein the first upstream pipe is formed by a plurality of pipes, and each pipe of the plurality of pipes is respectively connected to at least one of an exhaust port of the first cylinder and the third cylinder of the in-line 6-cylinder engine and the fourth cylinder and the sixth cylinder of the in-line 6-cylinder engine.
 14. The exhaust manifold according to claim 10, wherein the first upstream pipe forms a fan-shaped aperture plane in the merging pipe, and wherein semicircular or fan-shaped aperture plane corresponding to a downstream end of the exhaust path of the second upstream pipe is formed in the merging pipe.
 15. The exhaust manifold according to claim 10, wherein a gap is formed between the first upstream pipe and the second upstream pipe, a heat-insulating spacer is provided within the gap.
 16. The exhaust manifold according to claim 10, wherein the second upstream pipe is formed by a pair of sheet metal members that sandwich the first upstream pipe and that are hermetically joined each other.
 17. The exhaust manifold according to claim 16, wherein the merging pipe is formed by the pair of sheet metal members integrated with the second upstream pipe. 